To ensure steady extrusion of paste through a die, it is desirable to reduce static zones caused by abrupt contractions.
These static zones can be reduced by reducing the angle of the die entry, where 90 degrees is the maximum, in conventional macro-extruders. Conventional macro-extruders generally have a size large enough to allow sloped die entry using machining, molding, or other well-known methods. By contrast, a micro-extruder has a minimum channel cross-section of less than approximately 200 microns.
Due to the smaller channel size, previously unconsidered issues arise in micro-extruders. For example, the material in the ‘static zone’ can eventually dislodge and re-enter the extrusion stream and cause clogging of the extrusion nozzle. Also, blobs of weakly-agglomerated particles in the paste are more likely to be trapped at the steps, thus partially blocking the channel. In macro-extruders, the die entries are generally large enough relative to paste particle sizes such that this does not usually become a problem.